Lecture 4: Energy & Enzymes

Different types of systems Isolated System

o Doesn’t exchange matter or energy with its surroundings. Closed System

o Can exchange energy, but not matter, with its surroundings. Open System

o Both energy and matter can move freely between the system and the surroundings.

Laws of Thermodynamicso Energy cannot be created or destroyed but can be transformed. Example: Photons of

light being absorbed get turned into chemical energy.o Total disorder of a system and its surroundings always increase. Entropy, the

unavailability of a system's thermal energy for conversion into mechanical work.

Living things are not closed systems as they constantly bring in energy and matter. The energy brought in is required to keep making the complex molecules even though they’re broken down all the time the energy creates them again. Entropy is being fought against by bringing in energy and matter from the environment.

Entropy: How do you define, measure disorder…?Entropy = Energy spreading, dispersal. When energy moves from being localized to more spread out.

If you have a pool of amino acids the energy is spread out and when a protein is made the energy is localized.

Free Energy (G)How much can actually be used to do work? (Free Energy) ΔG = ΔH – TΔSThe change in free Energy = the change in enthalpy – Temperature (Change in Entropy)

Enthalpy the sheer heat content of a system, (+Endothermic) (-Exothermic)Entropy, (+More Spread Out) (-Less Spread Out)Free Energy, (+Endergonic) (-Exergonic)

In a system not all of the energy can be used because of entropy.Example: A B, If there is a negative change in the energy the reaction will be spontaneous or the reaction will occur all by itself and doesn’t need energy to do so.

B A, The energy will be opposite and not spontaneous.

Endothermic reactions CAN be exergonic, the melting of ice.

EnzymesEnzymes don’t provide energy but speed up reactions. Cannot make endergonic reactions go, ATP could supply energy.

A BExergonic, an enzyme can make this reaction go faster.

B CEnzyme cannot make an ender reaction go because they do not provide energy. It requires some kind of energy and the enzyme, however the enzyme DOES NOT change the thermodynamics.

ENERGY IS NOT RELEASED WHEN YOU BREAK BONDS BUT REQUIRED TO MAKE BONDS.

Enzymes lower activation energy of a reaction and the more energy available is more molecules going to the transition state because rate is proportional to the number of activated molecules.

Enzyme + Substrate = ES which then leaves the product and the enzyme. The catalytic cycle. At higher temperatures enzymes may work better because of more collisions between enzymes and substrates.